chore(repo): DX cleanup — categorise examples, text-diffable golden, build/ output (#27 #28 #30)

Repository-cleanup / DX pass folding three tracker items into one coherent
change, verified green end to end (`bin/x test` 49/0, `bin/x selfhost-test`
29/0, `bin/x test-tools` 29/0).

#28 — curate & categorise examples/
- 42 flat entries regrouped into intent-revealing subdirs: games/, rendering/,
  ecs/, events/, networking/, lang/, library/ (was lib/).
- chronorift dir-vs-file duplication resolved: the entry file and its import
  modules now live together under games/chronorift(.ludic).
- Every path reference updated repo-wide (test runner, editor-tool drivers,
  docs/site, design docs).
- New examples/README.md indexes the whole set with run commands.
- Showcase examples without a self-asserting entry (hello, events, net_rt) now
  get a compile-only rot guard in `bin/x test`, so nothing here rots silently.

#30 — text-diffable golden baseline
- The 4 binary selfhost/golden/*.ppm blobs are replaced by a single
  selfhost/golden/renders.sha256 manifest (SHA-256 per render). Hashes are
  byte-identical to the old PPMs, so the baseline is unchanged — only its form.
- game_case now compares framebuffer hashes; a regression shows as a changed
  hex line in review, not "binary files differ".
- New `bin/x golden` regenerates the manifest deliberately (review with
  `git diff selfhost/golden/renders.sha256`).

#27 — PPM & asset handling
- Headless renders now write build/out.ppm, never the repo root; `x app`,
  `x clean`, messaging and .gitignore updated to match. Nothing is written to
  the working root any more.
- Redundant local Kenney .zip archives removed (the art ships extracted;
  .gitignore already excludes *.zip). CC0 License.txt files retained.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/lang/offline_rewards.ludic

@@ -0,0 +1,29 @@
+# offline_rewards.ludic — issue #9's worked example: an idle/farming game grants
+# "you were away for N hours" rewards on load, using the Time/Date/Duration and
+# the deterministic Clock. Everything is integer seconds, so the result replays
+# identically — no wall clock, no floating point.
+#
+#   bin/ludic examples/lang/offline_rewards.ludic     # prints 13 / 650 / 2026-08-30 / 0
+program OfflineRewards {
+  entry {
+    # A save records when the player last quit. It is hardcoded here so the demo
+    # is deterministic; a real game writes Time.now() (or Clock.now()) at save.
+    let last_seen = DateTime.from(2026, 8, 29, 18, 30, 0)
+
+    # On load, set the game clock to "now". We drive it explicitly (rather than
+    # Time.now) so gameplay stays replay-safe and this sample is reproducible.
+    Clock.set(DateTime.from(2026, 8, 30, 7, 45, 0))
+
+    let away  = Clock.now() - last_seen         # a Duration in seconds (47700)
+    let hours = Duration.as_hours(away)         # whole hours away
+
+    # Reward: 50 coins per full hour, capped at a day's worth.
+    let capped = Math.min(hours, 24)
+    let coins  = capped * 50
+
+    print(hours)                                        # 13
+    print(coins)                                        # 650
+    print(DateTime.format(Clock.now(), "YYYY-MM-DD"))   # 2026-08-30 (the day they returned)
+    print(DateTime.weekday(Clock.now()))                # 0 = Sunday
+  }
+}